Process for purifying impure lead



Patented Mar. s, 1938 PROCESS FOR PURIFYING DIPUBE LEAD Ferdinand leferrer, Paris, France, usignor to Societe Miniere et Mtallurgillne dc Penalroya, Paris, France, a corporation of France No limit... Application October 25, 19:5,

rial No. 46,827. In France November 2, 1934 Claims- -(oi. 75-78) It is well known that most of the molten'alloys give when slowly cooled a series of solid products the composition of which varies in a continuous manner from the beginning to the end of the 5 solidification.

Only eutectic alloys do not follow this rule. It is thus often possible to modify the composition of an alloy and to obtain a more or less complete separation of its constituents through a partial solidification with a separationof the solid and liquid phases which are in presence, in well determined conditions. I This property has been used for a long time in metallurgical processes for the refining of metals. It has already been proposed to amplify this phenomenon and to render more efllcient the separation of the constituents by adding to the molten alloy, prior to the partial solidification, certain elements conveniently selected. Thus, by adding a sufilcient quantity of zinc to molten argentiferous lead it has been possible to obtain, by cooling in the neighbourhood of the temperature of solidification of the lead, a floating solid crust which it is easy to separate and which carries with itself the totality of the silver preexisting in the lead.

More recently it has been tried to separate the lead from its alloys by using additions of alkaline or earth-alkaline metals.

Now it has been found, according to this invention, that additions of small quantities of sodium and of zinc to impure leads in a molten condition (containing more particularly arsenic and/or copper and/or antimony) render it possible to 35 separate by cooling in the floating crust almost the totality of the arsenic and/or the copper and/or the antimony which were contained in the treated lead.

If the treated lead contains tin, silver and gold,

the content of these metals is not substantially modified.

Of course, if the lead under treatment already contains zinc, it will be possible to use only a simple addition of sodium (if the quantity of zinc 45 in the lead is sumcient); or it will be suilicient to complete the desired quantity of zinc through a smaller addition of this latter metal.

Zinc and sodium separate in the floating crust with the impurities which have been eliminated.

50 Sodium and/or zinc may be added to the treated lead, in the form of a pure metal or of an alloy.

As a nonlimitative example of a method for carrying theinvention into practice, by treatinga working lead (containing 0.1% of arsenic, 0.07% 55 of tin, 0.4% of antimony, 0.05% of copper and 0.1% of silver) in a molten condition through 0.7% of zinc and 0.5% of sodium, there is obtained after skimming at 330 0. (626 F.) a'lcad which still contains 0.07% of tin and 0.1% of silver, but contains less than 0.01% 0! arsenic, 5,

less than 0.02% of antimony and less than 0.005% p of copper.

This process'can also be used for purifying an alloy of lead and tin and for eliminating from the said alloy impurities such as: arsenic, antimony 10 and copper, in order toobtain an alloy of lead and tin which is practically pure.

Thus, by way of example, an alloy of lead and tin with 10% 0! Sn, 0.05% of As, 0.1% of Sb and 0.02% of Cu was purified by adding to it 0.8% 10 of zinc and 0.4% of sodium.

After the known treatment withwater steam, for instance in order to eliminate the excess of sodium, an alloy of lead and tin was obtained which contained 9.8% of tin and only 0.002% of 20 arsenic, 0.005% of antimony and 0.001% of copper.

This process can be combined with any other known process for purifying lead.

This process can be combined more particu- 25 larly with the process which is the subjectmatter of the patent application and with the known process (known as Parkes method) for desilvering lead through zinc. Thus a complete purification of lead will be obtained. Thus, as a nonlimitative example, a molten, working lead containing 0.5% ofarsenic, 0.7% of antimony, 0.05% of copper and 0.07% of silver has been treated first by an addition of 0.5% of .sodium. After skimming and treatment with water steam the lead contained no more than 0.01% of arsenic, 0.005% of copper. Its antimony content was still of 0.7% and its silver content. was still 'of 0.07%.

The lead then was treated by the Parkes meth- 40 od and a lead was obtained which contained less than 0.002% of arsenic, less than 0.001% of copper,'less'than 0.001% of silver and always 0.7% of antimony. The zinc content of this lead was 01 about 0.6%. A new addition of 0.5% of sodium gives, after skimming at about 330 C. (626 F.) and treatment with water steam, a soft lead having approximately the following composition:

arsenic less than 0.0002%; antimony less than 0.002%; copper less than 0.001% and containing less than 0.001% of silver.

what I claim is:

1. The method of purifying impure lead con taining antimony and at least one of the group consisting of copper and arsenic with or withou other impurities, which consists in adding sodi and zinc in predetermined proportions to the bath bath to cool whereby substantially all the antimony, copper and arsenic presand allowing the cut will be separated from the lead.

2. The method of taining tin and at sisting of antimony,

10 sodium and zinc in cool down, whereby copper, and arated from the lead and tin.

process in order to treating the lead thus 20 sodium in the presence the lead after the completion of the Parkes procpurifying impure lead conleast one of thegroup concopper, and arsenic with or without other impurities, which consists in adding predetermined proportions to a bath of said impure lead. allowing said bath to substantially all the anarsenic present will be sep- 3. A process for purifying impure lead containing antimony and silver, which consists in treating the lead in a molten state by the Parkes remove the silver therefrom, freed from-the silver with of the zinc remaining in um ess, said sodium and zinc being simultaneously bath, and removing the crust formed on top thereof.

4. .Procea for purifying impure lead containing antimony, substantially no silver but containing imbibition zinc which consists in adding to a bath lead a crust which is formed on top of the bath.

5. {for purifying lead containing metallic impurities and such an amount of tin that it can be considered as an impure lead-tin alloy, which consists in treating a bath of the said lead by. means of sodium and zinc, allowing the bath to cool down until a crust is formed on top of the bath, which practically all the metallic impurities, and separating the said crust from the purified lead-tin alloy.

FERDINAND present in predetermined proportions, cooling the 

